Background: Little is known about the nature of loss of negative growth controls in the context of human cutaneous melanoma, and how such losses may affect the development and malignant progression of the disease. In studies undertaken during the current grant period evidence was obtained for what may be three new important aspects of negative growth control (and its subversion) in human melanoma. These are: (i) fibroblast or endothelial derived (ie. paracrine) interleukin-6 (IL-6) can function in vitro as a potent growth inhibitor of melanoma cell lines established from early-stage curable primary lesions, whereas cell lines from more advanced, metastatically-competent, lesions are resistant to this inhibitory effect; (ii) in a significant subset (50-70%) of advanced-stage melanoma cell lines, IL-6 appears to be switched on and function as a mitogenic autocrine growth factor in vitro - a process we have termed "cytokine switching"; (iii) a number of other cytokines (IL-1, TGF-beta, TNF-alpha and oncostatin M) can also function in vitro as growth inhibitors for early-stage melanomas, whereas this effect is diminished or lost altogether with tumor progression - a phenomenon we have termed "multicytokine resistance". The Problem: All of the aforementioned results were obtained in vitro using established melanoma cell lines. The next logical phases of investigation are to investigate the significance of these in vitro findings to the experimental and clinical in vivo behavior of human melanomas, and the molecular mechanisms involved. Overall Guiding Hypothesis and Specific Aims: It is hypothesized that IL-6 resistance per se, multicytokine resistance in general, and IL-6 "cytokine switching" contribute to the malignant aggressiveness of human melanoma. The specific aims are: (i) to evaluate she capacity of paracrine and/or autocrine IL-6 to alter the growth of human melanomas in vivo (i.e. in nude mice), and ultimately to act as a growth stimulant; (ii) to evaluate the relative expression of IL-6 mRNA and protein in human melanoma tissue samples (at different stages of disease), and as possible prognostic indicators of melanoma aggressiveness; (iii) to determine the molecular characteristics of IL-6 signal transduction alterations responsible for IL-6 resistance in melanoma cells. Significance: The proposed experiments are significant in relation to several issues including: (i) helping to uncover part of the basis for the progression and pathogenesis of human cutaneous melanomas and, (ii) elucidating the role of "hemopoietic" cytokines and (loss of) negative growth controls in melanoma pathobiology. Although our experiments deal only with human melanoma they may have much broader relevance since it is now known that a diverse array of human carcinomas produce IL-6, the clinical significance of which is largely unknown.